1. Field of the Invention
This invention relates to a catalyst component or catalyst system that is useful for polymerizing or copolymerizing alpha-olefins and more particularly concerns a magnesium-containing supported titanium halide-based alpha-olefin polymerization or copolymerization catalyst component or catalyst.
2. Discussion of the Prior Art
Magnesium-containing supported titanium halide-based alpha-olefin polymerization or copolymerization catalyst components or catalyst systems containing such components are now well known in the art. Typically, these catalyst components and catalyst systems are recognized for their performance based on activity and stereospecificity. However, commercial olefin polymerization or copolymerization, especially gas-phase alpha-olefin polymerization or copolymerization, requires additional catalyst attributes for economical large-scale operation. Specifically, polymer or copolymer morphology is often critical and typically depends upon catalyst morphology. Good polymer morphology generally involves uniformity of particle size and shape, resistance to attrition and an acceptably high bulk density. Minimization of very small particles (fines) typically is very important, especially in gas-phase polymerizations or copolymerizations in order to avoid transfer or recycle line pluggage. Therefore, it is highly desirable to develop alpha-olefin polymerization and copolymerization catalysts and catalyst components that have improved morphology. For example, experience indicates that, in order to produce high ethylene content/high melt flow rate impact copolymers of ethylene and propylene having a median particle size of at least 1000 microns, it is necessary to employ a copolymerization catalyst having a median particle size of at least 35-55 microns. Another property which is important commercially is the maintenance of an acceptably high bulk density. Typically, this property is measured in pounds per cubic foot of polymer or copolymer.
Whatever the cause, production of small polymer particles and polymer of broad particle size distribution are disadvantageous for several reasons. From the standpoint of polymerization process efficiency, high levels of small polymer particles can cause problems because the particles tend to accumulate in, and plug, process lines and filters. From the standpoint of handling and processing of polyolefins, small polymer particles and broad particle size distribution can be disadvantageous because polymer bulk density often is lower than desired and an extrusion and/or pelletization step often is required prior to processing.
Numerous individual processes or process steps have been disclosed which have as their purpose the provision of improved supported, magnesium-containing, titanium-containing, electron donor-containing olefin polymerization or copolymerization catalysts. For example, the use of carbon dioxide in preparing a magnesium-containing support has been described in the aforementioned U.S. Pat. No. 4,540,679 as a means to improve control of the morphology of the catalyst and hence of the polymer product. Also, in a different context use of carbon dioxide was described in U.S. Pat. Nos. 4,246,383; 2,244,838; 4,529,715; and 4,530,915. Treating alcoholic solutions and suspensions of alkaline earth alcoholates with carbon dioxide or sulfur dioxide was noted in Chemical Abstracts, Vol. 76, 853050v (1972). Forming a soluble magnesium species has been described in U.S. Pat. Nos. 4,315,874; 4,399,054; 4,071,674; and 4,439,540. Examples of use of silicon compounds in formation of a catalyst component include U.S. Pat. Nos. 4,071,672; 4,085,276; 4,220,554; and 4,315,835. Tetrahydrofuran (THF) has been described variously to complex a magnesium chloride species (e.g., U.S. Pat. Nos. 4,482,687, 4,277,372, 3,642,746, and 3,642,772 and in European Pat. No. 131,832); as modifier in a cocatalyst (e.g., U.S. Pat. Nos. 4,158,642 and 4,148,756); and as a solvent (e.g., U.S. Pat. Nos. 4,477,639 and 4,518,706). However the specific combination of steps taught in this invention to produce a catalyst with extremely advantageous properties has not been disclosed.
Arzoumanidis et al., aforesaid U.S. Pat. No. 4,866,022 discloses a method for forming a particularly advantageous alpha-olefin polymerization or copolymerization catalyst or catalyst component that involves a specific sequence of specific individual process steps such that the resulting catalyst or catalyst component has exceptionally high activity and stereospecificity combined with very good morphology. A solid hydrocarbon-insoluble, alpha-olefin polymerization or copolymerization catalyst or catalyst component with superior activity, stereospecificity and morphology characteristics is disclosed as comprising the product formed by 1) forming a solution of a magnesium-containing species from a magnesium hydrocarboxyl carbonate or magnesium carboxylate; 2) precipitating solid particles from such magnesium-containing solution by treatment with a transition metal halide and an organosilane; 3) reprecipitating such solid particles from a mixture containing a cyclic ether; and 4) treating the reprecipitated particles with a transition metal compound and an electron donor. Alcohols that are useful in solvating magnesium carbonates and carboxylates are disclosed in column 4, lines 36-44 as including: "those having the structure HOR' wherein R' is an alkyl radical of 1 to about 18 carbon atoms, an aryl radical of 6 to about 12 carbon atoms or an alkaryl or aralkyl radical of 7 to about 12 carbon atoms. Typically, one or more alcohols containing from 1 to 12 carbon atoms can be used such as methanol, ethanol, propanol, isopropanol, tert-butyl alcohol, cyclohexanol, 2-ethylhexanol, dodecanol, and the like. Of these, 2-ethyl-1-hexanol is preferred." The ratio of the total number of moles of the alcohol employed-to-the magnesium hydrocarbyl carbonate or carboxylate from which the magnesium-containing species is formed in the examples in U.S. Pat. No. 4,866,022 is 1.32:1.
Arzoumanidis et al., aforesaid U.S. Pat. No. 4,540,679 disclose a process for the preparation of a magnesium hydrocarbyl carbonate by reacting a suspension of a magnesium alcoholate in an alcohol with carbon dioxide and reacting the magnesium hydrocarbyl carbonate with a transition metal component. Sufficient alcohol is employed to form a solution of the resulting magnesium hydrocarbyl carbonate in the alcohol. The ratio of the total number of moles of the alcohol employed-to-the magnesium alcoholate in the examples in U.S. Pat. No. 4,540,679 is 3.9:1 to 10.5:1.
Arzoumanidis et al., aforesaid U.S. Pat. No. 4,612,299 disclose a process for the preparation of a magnesium carboxylate by reacting a solution of a hydrocarbyl magnesium compound with carbon dioxide to precipitate a magnesium carboxylate and reacting the magnesium carboxylate with a transition metal component. Alcohols are not disclosed as suitable for use as a solvent or diluent in this process.
While each of the processes of the aforesaid U.S. Pat. Nos. 4,866,022; 4,540,679; and 4,612,299 affords alpha-olefin polymerization or copolymerization catalyst or catalyst components which have improved morphology and which afford polymer or copolymer products which also have improved morphology, it is highly desirable to develop additional alpha-olefin polymerization or copolymerization catalysts or catalyst components that have even further improved morphology and that afford polymers or copolymers especially the aforesaid impact copolymers, which also have even further improved morphology.